Conventionally, hydraulic pressure has been utilized for a drive source of an injection apparatus which performs injection by moving a screw in the axial direction thereof. Recently have been developed injection-molding machines which use a servomotor as the drive source of the injection apparatus. In this case, the servomotor must be increased in size, in order to make the injection-molding machines large-sized for a higher injection output. If the servomotor is increased in size, then it is a very special motor, which costs high. The moment of inertia, which greatly influences the rise- and fall-time performance of the motor, increases in proportion to the fourth power of the rotor diameter of the motor. If the servomotor used is large-sized, therefore, the moment of inertia is so high that it is very difficult, technically, to obtain a satisfactory acceleration/deceleration characteristic. Thereupon, a system has been proposed in which an injection mechanism is driven by mean of a plurality of motors (see Japanese Patent Disclosure No. 60-125618).